Electron beam convergence apparatus



April 17, 1956 H. c. GOODRICH ELECTRON BEAM CONVERGENCE APPARATUS 3 Sheets-Sheet l Fil 9d Oct. 25, 1954 ii \N lfimkrf @2322 April 1955 H. c. GOODRICH ELECTRON BEAM CONVERGENCE APPARATUS Filed Oct. 25, 1954 3 Sheets-Sheet 22 INVENTO R.

April 1955 H. c. GOODRICH ELECTRON BEAM CONVERGENCE APPARATUS 3 Sheets-Sheet 3 Filed Oct. 25, 1954 l N VE TOf.

WMM WWW ww Z 6 www a w \1 V 1? 4 z 7 i tip. 5 0V! PW i 4 4 /WM V 6 M i A H 6 W A E EM i m mm 7 0 W 5 F K ELECTRON BEAM CONVERGENCE APPARATUS Hunter C. Goodrich, Collingswood, N. .L, assignor to Radio Corporation of America, a corporation of Delaware Application October 25, 1954, Serial No. 464,497

Claims. (Cl. 31513) This invention relates to systems for controlling the electron beams of cathode ray tubes and particularly to systems in which a plurality of beams is deflected by a common deflection apparatus.

A cathode ray tube with which the present invention may be successfully employed is a color kinescope of the general type described in an article titled A three-gun shadow-mask color kinescope, by H. B. Law, published in the Proceedings of the I. R. B, vol. 39, N0. 10, October 1951, at page 1186. Such a tube has a luminescent screen as part of a target electrode structure in which difierent phosphor areas produce differently colored light when excited by electron beam components impinging upon it from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas. The invention also pertains to a kinescope of the type described in another article titled A one-gun shadow-mask color kinescope, by R. R. Law, published in the Proceedings of the I. R. 13., vol. 39, No. 10, October 1951, at page 1194.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the diflerent electron beam components at all points of the raster scanned thereby at the target electrode. In general, this convergence may be effected by means of apparatus such as that disclosed in an article titled Deflection and convergence in color kinescopes, by A. W. Friend, published in the Proceedings of the I. R. B, vol. 39, No. 10, October 1951, at page 1249. Such beam convergence apparatus includes an electron-optical system by which to control the beam convergence angles. The electron-optical system is variably energized as a function of the radial angle of beam deflection.

Another type of apparatus for controlling the convergence of a plurality of electron beam components at a target electrode structure and with which the present invention is more particularly concerned comprises, 'in general, a means for producing a plurality 'of electron beam components which traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube, and individual electromagnetic means located respectively adjacent to the pre-deflection beam paths and of such a character to be energizable as a function of the angular beam deflection in a manner to efiect the desired beam convergence. By such means, the beam convergence angle may be varied in a manner suitable to effect a satisfactory beam convergence at the target electrode at substantially all points in the scanned raster.

More particularly, it will be understood that the term beam components as used in this specification and in the appended claims denotes either a plurality of ,individual electron beams emanating, respectively, from a plurality of electron guns or from a single electron 'gun provided with suitable electronroptical, or other apparatus, 7

for forming three individual beams and, in addition, those components of a single electron beam to which is imparted a spinning motion so as to trace a substantially conic locus at ditferent positions thereof. Accordingly, the apparatus by which a plurality of such electron beam components is produced may include onthe one hand, three electron guns or, on the other hand, a single electron gun, together with the auxiliary apparatus by which the spinning motion is imparted to thebeam.

The particular electromagnetic beam convergence apparatus to which this invention pertains includes, for the respective beam components, a plurality of electromagnets each preferably having a pair of pole pieces located internally of the kinescope envelope. Each of the beam components passes between a different pair of internal pole pieces. The field produced between the pole pieces is of a character to move the beam components radially relative to the longitudinal axis of the tube. By energizing any one of the electromagnets differently from the rest, the beam component associated therewith may be moved radially independently of the others.

Because of the physical displacement of the beam components relative to one another, it is impossible for them to follow precisely identical paths through the region in which they are deflected to scan the usual rectangular raster. Also it is difiicult in practice to produce a rasterscanning electromagnetic deflection field which is precisely uniform throughout its extent. This is particularly so in those parts of the deflection field which are closely adjacent to the yoke windings which produce the field. It is seen, therefore, that all of the electron beam components may not be equally deflected in all parts of the raster, particularly in the corners where the beam, components come closest to the yoke windings. Accordingly, when the energization of the beam convergence apparatus is varied in the same manner for all beam components, as in the prior art,.there may be some misconvergence of the beam components in the corners of the raster, for example. 1

Accordingly, it is an object of this invention to effect a selective convergence of the individual beam components in a manner to produce a. substantially uniform beam convergence at all points in a scanned raster.

Another object of the invention is to provide the same convergence control for. all of a plurality of beam components for all points in a scanned raster, and additional convergence control for one or more of the beam componets for selected points in the raster.

In accordance with this invention, all of the electron beam components of a cathode ray tube are movedradially relative to the longitudinal axis of the tube substantially identically as a function of the angular deflection of the beam components for all points of a scanned raster and at least one of the electron beam components is additionally moved radially relative to the longitudinal tube axis as a function of the angular deflection for selected points of the raster. The additional radial beam movement is accomplished by means including an electromagnet mounted adjacent to the pre-deflection path of the additionally moved beam component and producing a field transverse to the pre-deflection beam path. Preferably all of the beam components are moved radially relative to the tube axis by individual electromagnets mounted adjacent to the respective pro-deflection beam paths.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the follbv'viiig description read in connection with the accompanying drawings.

In the drawings:

Figure 1 is a view showing the general arrangement of image-reproducing apparatus embodying one form of an electron beam convergence system in accordance with this invention;

' Figure 2 is a transverse cross-sectional view taken generally on the line 22 of Figure l and showing the arrangement of the beam convergence electromagnets;

Figure 3 is a diagrammatic illustration of the relative beam positions in different regions of the scanned raster;

Figure 4 is an exaggerated illustration of the misregistration of the diiferent rasters as a result of the relative beam positions shown in Figure 3;

Figure 5 illustrates the general character of typical wave forms needed tocorrect the kind of misregistration shown in Figure 4; and, v

Figure 6 is a schematic circuit diagram of apparatus in accordance with the invention for energizing the electromagnetic beam convergence magnets.

Reference first will be made to Figure l for a general description of an illustrative embodiment of electron beam convergence. system in accordance with the present invention. The system includes a tri-color kinescope 11 which may be of the same general type as that disclosed in the H. B. Law paper previously referred to. Itwill be understood, however, that the kinescope, alternatively, may be of other types such as that shown in the R. R. Law paper. In any case, however, the kinescope preferably has a luminescent screen 12 provided with a multiplicity of small phosphor areas arranged in groups and-capable respectively of producing light of the different component colors in which the image is tobe reproduced when excited by an electron beam. In back of and spaced from the screen 12 there is an apertured masking electrode 13 having an aperture for-and in alignment with each group of phosphor areas of the screen 12.

v In the particular tube illustrated, the kinescop'e also has a plurality of electron gun's, equal in number to the number of primary colors in which the image is tobe reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid and a focussing electrode. Since the three guns are identical, the. different parts thereof will be referred to collectively as the cathodes 14, the control grids 15, and the focussing electrodes 16. The three electron guns produce schematically represented beams B, R' and G by which to energize, respectively, theblue, red and green .phosphor areas of the screen 12. When these electron beams are properly converged at the masking electrode 13'they pass through the apertures thereof from different-directions and impinge upon different'phosphbr areas of the various groups so as to produce blue, red and green light. It is to benoted that the size of the phosphor areas, the angles between the beams and the spacing of the mask 13 from the screen 12 as compared withv the length of the tube are exaggerated for better illustration of the operation of the kinescope.

The electron-optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in the present instance, of a conductive wall coating 20 formed onthe inner surface of the tubular glass neck 21 of the kinescope extending from the region adjacent to the outer end of the focussing electrodes 16 to the conical section 22 of the tube which in this case is metallic. Suitable electrical connection (not shown) is made' at the junction of the wall coating with the nietal'cone 22. Preferably, the target electrode structure, including the masking electrode 13 and the luminescent screen 12 which for this purpose may be metallized, is electrically connected to the metal cone 22 by suitable means. (not shown). Metallizaticn of a luminescentscreen of the character described may be effected in the manner disclosed in a paper by D. W. Epstein and L. Pensak titled Improved azaleas ray tubes with metal-backed liiinines cent screens, published in the RCA Review, vol. VII, March 1946, at pages 5-10.

The described electrode structure of the kinescope may be energized in a conventional manner such as that illustrated. The source of energy is represented by a battery 23 across the terminals of which there is connected a voltage dividerw24. The cathodes 14 are connected to the grounded point of the voltage divider and the control grids 15 are connected to a point'which is somewhatnegative relative to ground. Similarly, the fccussing electrodes 16 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 3000 volts positive relative to the grounded cathodes. Also the beam-accelerating anode, including the wall coating ,and metal cone 22, is connected to the voltage divider 24 at a point which may conventionally be approximately 18,000 volts positive relative to the grounded cathodes.

The electron beams B, R and Gate modulated suitably in intensity under the control of color-representative video signals derived from a source 25; It will be understood that the video signal source is represented herein entirely diagrammatically since it does not form an essential part of the present invention. The signal source 25 usually will be part of a signal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be acolor television camera in the event that the kinescope 11 is employed as .a monitor, for example. Also, it will be understood that the illustrated connected of the video signal source 25 to the electron guns of the kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14. Instead, it will be understood, that they may be made to the grids 15 or, in accordance with other modes of operation of color image-reproducing apparatus, the video signal source may be connected both to the cathodes and to the control grids of the electron guns.

Also associated with the color kinescope 11 is a'defiecti on yoke 26 which maybe entirely conventional including two, pairs of suitably placed coils electrically connectedtogetherin such a manner that, when properly energized, electromagnetic fields are produced, whereby to efiectbothhorizontal and vertical angular deflections of the electronbeams so as to scan the usual rectangular raster.. Energization ofthe deflection coils comprising the yoke 26 may be efiected by conventional vertical and horizontal deflection wave generators 21 and 28, respectively (see Figure 6). Such apparatus 1 will be understood to function suitably to produce substantially sawtooth current at'bothhorizontal and vertical deflection frequencies so that the fields produced by the yoke 26 are'varied inasubstantially sawtooth manner.

The I beam convergence system, in accordance with the present, invention, also includes a plurality of electromagnetic'field producing elements such as the magnets 29 and 30 mountedaround theneck 2 1 of the color kinescope adjacent the pre-defiection paths of the electron beam components. It: is to be understood that the precise location of these magnets is not necessarily indicated in this figure. Instead, as will appear in greater detail from a subsequent portion of the specification, it is to be understood that each of these magnets is located relative to] one of the electron beam components so a to infiuence its associatedbeam component to the virtual exclusionof the,other s Furthermore, it is to be understood that these magnets are of a character which, when suitably energized, produced respective fields which are transverse to the associated beam paths, and in directions to move the associated beam, componentsradially relative to the longitudinal axis of the kinescope 11.

.stantially at the apertured masking electrode 13. der to do this, the unidirectional energization of these .be individually energized in different magnitudes. effecting this initial beam convergence, it is to be under- .stood that the beams may be in any desired one of their different deflected positions. initially converged at the center of the raster to be :scanned. Alternatively they may be initially converged at one corner of the raster.

pair of spaced pole pieces and at least one energizing winding. Preferably two windings are provided for each of the electromagnets for separate energization. These features will be described subsequently in greater detail.

Before describing the details of the convergence system with which the present invention is related, a brief description will be given of the general manner in which the apparatus functions to produce the desired results. The convergence magnets such as 29 and 30 are energized by substantially unidirectional energy so as to effect an initial convergence of the electron beam components sub- In ormagnets is effected in such a way that the magnets may In For example, they may be The convergence magnets such as 29 and 30 also are dynamically energized by the control wave energy derived from a suitable generator (not shown in Figure 1) so as to effect a variation in the magnitude of the transverse fields produced respectively thereby. These field strength variations are in accordance with a predetermined function of the angular beam deflection. Variations in the strength of the fields produced by the convergence magnets such as 29 and 30 effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components so as to produce the desired convergence of the beam components substantially at the masking electrode 13.

For a further description of this type of beam con vergence apparatus, reference now will be made to Figure 2 of the drawings. This figure shows more clearly the relative positions of the convergence magnets, such as 29 and 30, and, additionally, 31, relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam B, is provided with a core having a body portion 32 and two external pole pieces 33 and 34. The pole pieces are mounted so as to be in close association with the tube neck 21. Also, as indicated in Figure l, the pole pieces extend for some distance longitudinally of the tube substantially as indicated. The magnet also is provided with an energizing coil structure 35 mounted upon the body portion 32. The energizing coil 35 preferably is provided with two windings, one primarily for static energization and the other for dynamic energization in a manner to be described subsequently. The convergence magnet 29 produces a field which, in the vicinity of the electron beam B, is substantially transverse to-the axis of the kinescope. By means of such a field, the electron beam B may be moved radially toward or away from. the longitudinal tube axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the coil 35.

In Figure 2, it also is illustrated that for each of the magnets there are provided on the inside of the tube neck 21 extended pole pieces so as to increase the efiectiveness -.of these magnets. The magnet 29, for example, is provided with a pair of inwardly extending pole pieces 36 and 37, associated respectively with the external pole pieces 33 and 34. By such means, it is seen that the resame position.

A general representation of the relative beam positions i'n-difierent regions of the scanned raster is shown in Figure 3, to which reference now will be made. The rectangular raster 38, which is scanned by the three electron beams at the target electrode structure of the kinescope 11, has generally the usual 4-to-3 aspect ratio. The positions of the three beams are shown in greatly exaggerated form in this figure for the purpose of clarity. It will be understood that, even though the beam positions are shown as being separate for the three different beams, in general all three beams will occupy very much the The beam array 39 at the center of the raster will be assumed to be proper for the desired rendition of the different image colors. It is seen that the red, green and blue beams R, G and B, respectively, are, in effect, located at the apices of an equilateral triangle. When convergence control of these beams is effected, it will be understood that they will effectively merge at the center of this triangle. The same general triangular relationship of the three electron beams is maintained at all points of the raster 38.

For illustrative purposes, the positions occupied by the three beams at the four corners of the raster have been shown again in a grossly exaggerated manner. The beam array 41 at the upper left-hand corner of the raster 38 is seen to have the blue and green beams B and G, respectively, positioned somewhat as they should be, but the red beam R is located at a point which is higher than it should be for proper excitation of the phosphor screen. In a somewhat analogous manner, it is seen that the beam array 42 at the upper right-hand corner of the raster 38 has the red and blue beams R and B appearing in their proper positions and the green beam G is higher than it should be. The beam array 43 at the lower lefthand corner of the raster 38 is such that the blue and green beams B and G, respectively, are properly positioned, but the red beam R is lower than it should be. Likewise, in the beam array 44 at the lower right-hand corner of the raster, the red and blue beams R and B, respectively, are properly positioned, but the green beam G is lower than it should be.

The result of these changing relative positions of the electron beams is that the red, blue and green rasters are not in exact register throughout their respective areas. For the purposes of illustration of the present form of the invention, it will be assumed that the blue raster is satisfactory. The distortions produced in the red and green rasters are shown to an exaggerated degree in Figure 4, to which reference now will be made. The red raster 45, shown by the solid line enclosure, is seen to be higher at the upper left-hand corner than the green raster 46, shown by the broken line enclosure. The upper right-hand corner of the green raster is higher than the corresponding part of the red raster. Also, at thelower left-hand corner, the red raster is lower than the green raster. Similarly, at the lower right-hand corner, the green raster is lower than the red raster. It is seen that these raster distortions correspond in general to the misalignment of the red and green beams relative to one another and to the blue beam described with reference to Figure 3.

In Figure 4, it will be understood that the leftand right-hand edges of the red and green rasters coincide and that no substantial distortion exists in this area. These edges of the rasters have been shown displaced for greater clarity of illustration. It also will be understood that the raster distortion as illustrated in Figure 4 does not necessarily exist throughout only one-half of the raster, as might be inferred from this figure. For example, the red raster 45 does not necessarily become substantially horizontal in the right-hand portion thereof. It appears to be somewhat easier to understand the underlying principles of the present invention by assuming the existence of the conditions which are illustrated in Figure 4. The

extension of these principles to the other halves of the raster may be ma'd'eby those skilled the art by suitably varying the operating conditions of the apparatus which is to be described for effecting the desired corr tions.

In Figure 5, there are illustrated the general types of waveforms required to correct the type of raster distortion shown in Figure 4. These Waveforms may be applied to the beam convergence apparatus in addition to the substantially parabolic waves applied to such apparatus for the purpose of effecting dynamic cover'gence of the electron beams. The waveforms 47 and 48 of Figure are those suitable for the correction of the.

green and red rasters, respectively, at the lower corners thereof. It will be noted that the waveforms include substantially sawtooth components, such as 49 and 50, for example. In the case of the green correcting waveform 47, the sawtooth components 49 cm substantially only during the second half of the horizontal line scanning periods since it has been assumed that it is only during this portion of the horizontal lines that the raster distortion exists. In a similar manner, the sawtooth components 50 of the correcting wave 48 occur during the first half of the horizontal line scanning'periods for the reason that the red raster distortion has been assumed to occur only during the first half of the raster. Also, it will be noted that the sawtooth components 49 and 50 of the green and red correcting waveforms 47 and 48, respectively, occur only during the time in which the lower half of the raster is being scanned. Inasmuch as it is the nature of the kind of raster distortion which is to be corrected by means-of the present invention to become greater as portions of the raster further removed from the center are scanned, the sawtooth components 49 and 50 are seen to have increased amplitudes as lines further removed from the center of the raster are scanned.

It will be apparent to those skilled in the art that a similar correction of this type of raster distortion may be effected relative to the upper corners thereof by the use of waveforms similar to those described with reference to Figure 5. In such a case, the waveforms will include sawtooth components for use when horizontal lines near the top of the raster are scanned. It has been found, however, as a practical matter, that the raster distortion in the upper part of the raster is ordinarily not as severe as it is in the lower portions of the raster. Hence, in most cases, no distortion correction is needed for the upper portions of the raster.

Reference now will be made to Figure 6 of thedrawings for a description of the apparatus by which the beam controlling elements may be energized to effect both static and dynamic convergence of the plurality of electron beam components and also the correction of the type of raster distortior described with reference to Figures 3 and 4. The blue, red and green convergence magnets 29, and 31 each are provided with two windings designated, respectively, as static and dynamic windings. The blue, red and green convergence magnets are provided, respectively, with static windings 52, 53 and 54. Similarly, these magnets are provided with dynamac windings 55, 56 and 57. The energizing circuit for the static convergence windings 52, '53 and 54 includes a series circuit of resistors 58, 59 and 60 which may be connected as indicated between the positive terminal +8 of a grounded power supply'and its load. Preferably, these resistors are adjustable so as to enable the individual control of the energizing currents for the associated static windings of the convergence magnets 29, 30 and 31, re-

spectively. l v

The dynamic windings 55, 56 and 57 of the blue, red

and green convergence magnets 29, 30 and 31, respectively, are connected in series with one another and to vertical and horizotal convergence wave generators 62 and 63, respectively. These convergence wave generators may be 'of any suitable type, such as thatfdisclosed in Patent 2,672,574, granted March 1 6, 1954,:to I. E. Evans for Magnetic Beam Controlling System. 'In general,

estates the sfubstantially saw'tooth wave energy 64 of field frequeas whieh is derived from the conventional vertical deflection wave generator-"27 for encrgi'za-tion of the vertical deflection coils of the yoke 26 is converted by means of the vertical convergence wave generator '62 into a substantially para-bone current wave 65. This parabolic wave is coupled by means including acapacitor-66 to the series connection of the dynamic windings of the convergence magnets. Ina substantially similar manner, the line frequency sawtooth wave energy-67 derived from the conventional horizori tal defiection wave generator 28 for the energiz ation "o'f "the horizontal windings of the deflection yoke "26 is 'converted by the horizontal convergence wave generator 63 in 'a substantially parabolic current wiave -68 for impression by means including a capacitor 69 upon the dwnamic windings-of the'beam convergence electromagnets. By such means, it is seen that the convergence magnets are energized dynamically as functions of both vertical and horizontal beam deilection angles so as toe'ffect -substantiallyconvergence of the electron "beam components at all points in the raster scanned at the target electrode of the color kine,

scope 11 of Figure 1.

'The'st'aticwindings53 and 54, respectively, of the red and green convergence magnets 30 and 31 also are dynamically energized by waves having generally'the form of the waves 47"a-nd ofFigure 5. Such waves may be p'ro'duced'in accordance with the present invention by suitably ene'i'gizing an electron tube circuit of the kind rio'wto be d'escribed. The horizontal sawtooth wave 67 "de'rived'from the deflection wave generator 28 is coupled by "means including a capacitor 71 and a iistor 72 to the-control grid ofa phase splitting electron tube73. Lo'ad'resistors 74-and 75 connected, 'respe ctiv'ely, in the anode and cathode circuits of the tube 73am effective under the control of the horizontal sawtooth wave 67 to produce horizontal sawtooth waves '76"and"77 of opposite phases -'respectively at the anode and cathode of the tube 73. The horizontal frequency 'sawtoothwave 76 is impressed by means including a capacitor 78 a'nda resistor'79 uponthe control grid of a'green raster correcting electron-tube- 81. In a like manner, the opposite phase horizontal frequency sawtooth wave 77 isimp'ressed "by'means including a capacitor-82 anda resistor83 'iipon a red raster correcting electron tube'8'4. Alsojthe vertical frequency deflection wave 64'deriv'ed from the generator 27 is impressed by means including a capacitor ,85- and a resistor 86 upon the suppressor grids of the green and red raster correcting tubes 81fand'84. V

The suppressor grid 'circuits of the tubes; 81 and 84 are negativelyhiased'by means such as indicated by a battery 87 so as to"permit electron current flow to the respective anodes of the tubes only during the peak portions: of the vertical sawtooth wave 64. This corresponds 'in time to that in which'the'lower half of the raster is 'scanned. Thusfitisfs'eenthat by such biasing of these grids, the 'rast'erdistortion correcting waveforms are applied to the beam convergence apparatus only while the lower half of 'the ra'ster 'i's' being scanned so asto correct the distortion 'oc'curring'in the'lowercorncrs of the red and greenras'ters,

'The control grid'ofthe green raster correcting tube 81 isbiasednegativeIy by'means'indicated as a'battery 88 so that electron beam currentfiow' is'elfected only during the times when the-inve'rted horizontal sawtooth wave 76 has an amplitude corresponding to the scansion of the Thus, it is seen thatthe-tube 81 is operative only during the scansion of the-'left -hand -halves' ofthe-horizontal raster lihesand "then' only during the scansion of those raster lines lying inthe'lo'werhalf of the raster.

*In alike'niarinergthe r'edi'aster correctingtube 84 is biasednegatively by-m'eans represented as a battery '89 response to those portions of the horizontal frequency sawtooth wave 77 corresponding to the scansion of the right-hand halves of the horizontal lines of the raster. By such means, it is seen that the red raster correcting tube 84 is rendered operative only during the scansion of the right-hand halves of those horizontal lines lying in the lower half of the raster.

There are developed, therefore, at the respective anodes of the tubes 81 and 84 waveforms 47 and 48 corresponding to those shown in Figure 5. These waveforms are impressed upon the static windings 53 and 54 of the convergence magnets 30 and 31, respectively, by the illustrated coupling capacitors 91 and 92 connected between the anodes of the tube and the static convergence windmgs.

In order to minimize interaction of the modulated corrective waves 47 and 48 between the static windings 52, 53 and 54 and also to avoid the short-circuiting of these waves by the control resistors 58, 59 and 60, isolating choke coils 93, 94 and 95 are connected between the windings 52, 53 and 54 respectively and their associated control resistors 58, 59 and 60, respectively. Also, these static windings are bypassed to ground by capacitors 96, 97 and 98 so as to provide a return circuit for the Waves 47 and 48. Alternatively, tertiary windings may be mounted on the red and green magnets 30 and 31 and connected, respectively, in series in the plate circuits of the tubes 81 and 84.

It may be seen from the foregoing description of an illustrative embodiment of the invention that there is provided convergence apparatus for a plurality of electron beam components of a cathode ray tube by means of which all of the electron beam components are moved radially relative to the longitudinal axis of the tube substantially identically as a function of the angular deflection of the beam components by which a raster is scanned at a target electrode. Also, by means of this apparatus, at least one of the electron beam components is additionally moved in a radial manner relative to the longitudinal tube axis as a function of the angular beam deflection for selected points of the raster.- By means of such additional movement of one or more of the electron beam components, a correction is effected for such distortions of one or more of the rasters scanned by the individual beam components whereby mis-registration of the plurality of rasters might otherwise be produced. The common, as well as the selective movements of the plurality of electron beam components is effected by means of a plurality of electromagnets mounted respectively adjacent to the paths of the different electron beam components so as to produce a field which is transverse to the path of each of the beam components.

What is claimed is:

1. Convergence apparatus for a plurality of electron beam components of a cathode ray tube, wherein said beam components traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube and are angularly deflected to scan a raster at a target electrode structure, said convergence apparatus including: a plurality of electromagnets respectively mounted adjacent to said pre-deflection beam paths and energizable to produce respective fields transverse to said beam paths and in directions to move said beam components radially relative to said longitudial tube axis; means coupled to all of said electromagnets to variably energize all of said electromagnets substantially identically as a function of said angular deflection for all points of said raster; and means coupled to at least one of said electromagnets to variably energize said one electromagnet additionally and diiferently from at least one other of said electromagnets as a function of said angular deflection for selected points of said raster.

2. Convergence apparatus for a plurality of electron beam components of a cathode ray tube, wherein said beam components traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube and are-angularly deflected to scan a raster at a target electrode structure, said convergence apparatus including: a plurality of electromagnets respectively mounted adjacentto said pre-deflection beam paths and energizable to produce respective fields transverse to said beam paths and in directions to move said beam components radially relative to said longitudinal tube axis; means coupled to all of said electromagnets to variably energize all of said electromagnets substantially identically as a function of said angular deflection for all points of said raster; and means coupled to two of said electromagnets to variably energize said two electromagnets additionally and differently from another of said electromagnets and from each other as respective functions of said angular deflection for different selected points of said raster.

3. Convergence apparatus for a plurality of electron beam components of. a cathode ray tube, wherein said beam components traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube and are angularly deflected to scan a raster at a target.

electrode structure, said convergence apparatus including:

a plurality of electromagnets respectively mounted adja-- cent to said pre-deflection beam paths and energizable to produce respective fields transverse to said beam paths:

and in directions to move said beam components radially relative to said longitudinal tube axis; means coupled to all of said electromagnets to variably energize all of said electromagnets substantially identically as functions of said horizontal and vertical deflections for all points of said raster; means coupled to a first one of said electromagnets to variably energize said first electromagnet as a function of said angular deflection for a first group of selected points of said raster; and means coupled to a second one of said electromagnets to variably energize said second electromagnet as a function of said angular deflection for a second group of selected points of said raster.

4. Convergence apparatus for a tri-color kinescope wherein three electron beams traverse pre-deflection paths that are spaced symmetrically about the longitudinal axis of the kinescope and are angularly deflected both horizontally and vertically to scan a" common rectangular raster at a target electrode structure including a luminescent screen having phosphors capable of producing three different colors of light when excited by said respective electron beams, said convergence apparatus including: three electromagnets respectively mounted adjacent to said predeflection beam paths and energizable to produce respective fields transverse to said beam paths and in directions to move said electron beams radially relative to said longitudinal kinescope axis; means coupled to all three of said electromagnets to variably energize all three of said electromagnets substantially identically as a function of said angular deflection for all points of said raster; and means coupled to two of said electromagnets to variably energize said two electromagnets additionally and differ-- ently from said third electromagnet as a function of said"v angular deflection for selected points of said raster.

with said red and green light-producing beam paths in the same horizontal plane on one side of said axis and said blue light-producing beam path in another horizontal plane on the other side of said axis, are angularly deflected both horizontally and vertically to scan red,

green and blue rasters at said screen, said convergence 7 apparatus for effecting substantial registration of said red,

green and blue rasters including: three electromagnets;

11 respectively mounted adjacent to said pie-deflection beam paths and energizable to produce respective fields transverse to said beam paths and in directions to move said electron beams radially relative to said longitudinal kinescope axis; means coupled to all three of said electromagnets to variably energize all three of said electromagnets substantially identically as a function of said angular deflection for all points of said respective rasters; and means coupled to the two of said electromagnets respectively adjacent to said red and green light-producing beams to variably energize said two electromagnets additionally and differently from said electromagnet adjacent to said blue light-producing beam as a function of said angular deflection for selected corner portions of said red and green rasters.

References Cited in the file of this patent UNITED STATES PATENTS 

